ABSTRACT Metactive Medical is developing the Blockstent Microcatheter?, an innovative medical device for endovascular occlusion of peripheral arteries and veins. The device uses an expandable, detachable, gold metal balloon that can be delivered using a highly flexible, low profile, over-the- wire microcatheter, addressing an unmet medical need for a device that is easy to use and delivers immediate, complete, and lasting vessel occlusion in a wide variety of clinical indications. In a highly successful Phase I SBIR preclinical research program using canine artery occlusion models, the Blockstent Microcatheter allowed rapid and precise device placement and provided faster, more complete, and more sustained occlusion than commercially available, market leading coils and vascular plugs. In one arm of the study, the axillary arteries of four dogs were treated bilaterally using a 6 mm Blockstent on one side and a 6 mm Amplatzer Vascular Plug II (AVP2) on the other side. Acutely, all four Blockstent treatments resulted in immediate and complete vessel occlusion by angiography, while all four AVP2 treatments required ? 30 minutes to achieve vessel occlusion. At 28 days, all four Blockstent treatments demonstrated 100% occlusion whereas all four AVP2 treatments showed rapid, direct flow through device. In a second arm of the study, the internal thoracic arteries of four dogs were treated bilaterally using a 4 mm Blockstent on one side and a 4 mm Amplatzer Vascular Plug IV (AVP4) on the other side. Acutely, all four Blockstent treatments resulted in immediate and complete vessel occlusion by angiography, while all four AVP4 treatments required ? 30 minutes to achieve vessel occlusion. At 28 days, three of four Blockstent treatments demonstrated 100% occlusion whereas all four AVP4 treatments showed rapid, direct flow through device. In an acute study of eight dogs with induced right carotid artery bleeding, three of four 6 mm Blockstent treatments demonstrated immediate cessation of flow and bleeding after placement of a single device, with a fourth showing a minimal amount of residual bleeding that was stopped by placing a second device. All four of the 6 mm AVP2 treatments showed blood flow through the device and rapid bleeding after device placement, and three of four treatments showed blood flow through the device and bleeding at the end of the five-minute observation period. The proposed Phase II SBIR program would fund the development of a quality management system at Metactive, in vitro and in vivo design verification and validation studies, and US and EU regulatory filings to support the market launch of the Blockstent Microcatheter.